Reentry vehicle stripline slot antenna

ABSTRACT

A reentry vehicle antenna which is comprised of a stripline slot antenna with the antenna element including a stripline circuit board with a radiating aperture fed by a conventional strip transmission line. A feedback circuit is provided to control the input impedance of the antenna while operating into an RF transparent window as the window depth varies due to erosion upon reentry.

umreu mates Patent [191 v [111 ,82 ,05 Herskind [4 July 30, 1974 REENTRY VEHICLE STRIPLINE SLOT ANTENNA Primary Examiner-Eli Lieberman Attorney, Agent, or Firm-Harry A. Herbert, Jr.; [75] Inventor. figsard E. Herskind, Burlington, George Fine [73] Assignee: The United States of America as represented by the Secretary of the Air Force, Washington, DC. [5 7] ABSTRACT [22] Filed: July 24, 1973 A reentry vehicle antenna which is comprised of a [21] Appl' 382252 stripline slot antenna with the antenna element including a stripline circuit board with a radiating aperture [52] U.S. Cl 343/708, 343/768, 343/872 vfed y a n enti nal strip transmission line. A feed- [5|] Int. Cl. H0lq 13/10 a r ui is p ov ded to control the input impe- [58] Field of Search 343/708, 767, 768, 771, dance of the antenna while operating into an RF trans- 343/872 parent window as the window depth varies due to erosion upon reentry.

(56] References Cited UNlTED STATES PATENTS 3 Claims, 3 Drawing Figures 3.653.052 3/1972 Campbell et al 343/708 PAIENTmJuLsmsM F l E 1' IELZ 1 REENTRY VEHICLE STRIPLINE SLOT ANTENNA BACKGROUND OF THE INVENTION This invention provides control of the input impedance of a stripline slot antenna while operating into an RF transparent window as the window depth varies due to erosion upon reentry. Prior attempts to solve this problem typically utilized conventional matching techniques in an optimized manner with limited success. Principally, the disadvantage of the conventional techniques is that of limited control of the impedance as a function of ablation.

SUMMARY OF THE INVENTION A reentry vehicle antenna is provided in which the basic antenna element is a stripline circuit board on which is etched the prime radiating aperture. The aperture is fed by a conventional strip transmission line terminated at the aperture in a short circuit to the upper ground plane of the printed circuit board. A preselected feedback circuit which connects the antenna output circuit to the input circuit is utilized to provide an automatic control of the varying input impedance.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a view perspective of the prior art reentry vehicle stripline slot antenna;

FIG. 2 shows a top view of the reentry vehicle stripline slot antenna of the present invention including the basic circuit of FIG. 1 and a passive antenna feedback; and

FIG. 3 shows a side view of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring to FIG. 1, there is shown the prior art reentry vehicle stripline slot antenna. The basic antenna element is stripline circuit board 1 on which is etched prime radiating aperture 2. Prime radiating aperture 2 is fed by conventional strip transmission line 3 terminated at the aperture in a short circuit to upper ground plane 4 of the printed-circuit circuit board. Stripline transmission line 3 is provided with input connector 5 which is the impedance reference point. There is also shown RF transparent window 6 and cavity lower boundary 7 and 7a.

Now referring to FIG. 2, the invention utilizing antenna feedback, hereinafter referred to as PAF (passive antenna feedback) utilizes the basic antenna described in FIG. 1 and adds a feedback circuit 8 which connects the antenna output circuit 9 to the input cir' cuit. Feedback circuit 8 is comprised of etched strip transmission line 8 and terminating resistor 8b. Strip transmission line 8a is connected to radiating aperture 6 and is terminated by resistor 8b. Antenna output circuit 9 is equivalent to prime radiating aperture 2 of FIG. 1. Strip transmission line 8a is positioned adjacent to main (prime) feed transmission line 12 in the region of input circuit and couples energy from radiating aperture 6 to transmission line 12.

In the operation of the PAP circuit, a portion of the incident voltage, E @when arriving at radiating aperture 9 experiences reflection resulting in a voltage E 9 which propagates toward source 10. Source 10 also referred to as the input circuit is the equivalent of input terminal 5 of FIG. 1. Changes in dimension d of RF window 11 cause a change in the magnitude and phase of E 0, which results in a change in the resonant frequency of the antenna. Dimension d is clearly illustrated in FIG. 3.

The PAF circuit compensates for the change in E \1 due to changes in d by coupling a portion of the voltage E, Lilcoupled into the radiating slot (either by direct excitation or reflection from the window/air interface, or a combination of both) and feeding it back into main feed transmission line 12 in a phase and magnitude which compensates for the natural E Owhich originates at the radiating aperture feed point. Main feed transmission line 12 is equivalent to conventional strip transmission line 3 of FIG. 1. The net result is a relatively constant resonant frequency as the window dimension changes, and a corresponding low net value of E \ior, equivalently, a low VSWR as seen by the source.

It is noted that there are alternate methods of construction of the passive antenna feedback of the present invention. However, the basic theory and operation has been hereinbefore described in relationship to FIGS. 2 and 3. There is thus provided a reentry antenna having impedance control with negligible volume and relatively negligible weight penalties in construction. The invention also offers a simplistic approach to increase in impedance bandwidth and improved bandwidth over an extended range of window ablation.

What is claimed is:

1. A reentry vehicle stripline slot antenna operating into an RF transparent window comprising a stripline circuit board having an upper ground plane, a prime radiating aperture etched on said stripline circuit board, said prime radiating aperture operating into said RF transparent window, a prime strip transmission line positioned on said stripline circuit board and terminated at said prime radiating aperture in a short circuit to said upper ground plane, said prime strip transmission line feeding said prime radiating aperture, input circuit means for said strip transmission line, and a feedback circuit between said prime radiating aperture and said input circuit means to couple a portion of the voltage coupled into said prime radiating aperture and feeding back into said prime strip transmission line to control the input impedance of said stripline slot antenna as the window depth of said RF window varies due to erosion upon reentry.

2. A reentry vehicle stripline slot antenna as described in claim 1 wherein said feedback circuit is comprised of a second strip transmission line coupled into said prime radiating aperture and positioned to couple into said prime strip transmission line in the region of said input circuit means.

3. A reentry vehicle stripline slot antenna as described in claim 2 further including resistor means terminating said second strip transmission line. 

1. A reentry vehicle stripline slot antenna operating into an RF transparent window comprising a stripline circuit board having an upper ground plane, a prime radiating aperture etched on said stripline circuit board, said prime radiating aperture operating into said RF transparent window, a prime strip transmission line positioned on said stripline circuit board and terminated at said prime radiating aperture in a short circuit to said upper ground plane, said prime strip transmission line feeding said prime radiating aperture, input circuit means for said strip transmission line, and a feedback circuit between said prime radiating aperture and said input circuit means to couple a portion of the voltage coupled into said prime radiating aperture and feeding back into said prime strip transmission line to control the input impedance of said stripline slot antenna as the window depth of said RF window varies due to erosion upon reentry.
 2. A reentry vehicle stripline slot antenna as described in claim 1 wherein said feedback circuit is comprised of a second strip transmission line coupled into said prime radiating aperture and positioned to couple into said prime strip transmission line in the region of said input circuit means.
 3. A reentry vehicle stripline slot antenna as described in claim 2 further including resistor means terminating said second strip transmission line. 